Biological Psychology I: Genetics, Nervous System Cells, and Neurotransmitters

Biological Psychology I

Overview

This study guide covers foundational topics in biological psychology, focusing on the genetic basis of behavior, the cellular structure of the nervous system, and the role of neurotransmitters. Understanding these concepts is essential for exploring how biology influences psychological processes.

Genetics

Introduction to Genetics

Genetics is the study of how genes and the environment influence physical and behavioral traits. In psychology, genetics helps explain individual differences in behavior, cognition, and susceptibility to mental health conditions.

• Genes: Segments of DNA that contain instructions for building proteins, which influence the structure and function of the body and brain.

• Chromosomes: Structures within cells that contain a person's genetic material. Humans typically have 23 pairs of chromosomes.

• Genome: The complete set of genes or genetic material present in a cell or organism.

• Genotype: The genetic makeup of an individual.

• Phenotype: The observable physical and behavioral characteristics resulting from the interaction of genotype and environment.

Example: Eye color is determined by specific genes, but environmental factors can influence traits such as intelligence or personality.

Gene Editing and Epigenetics

Recent advances in biotechnology have made it possible to edit genes, raising ethical and practical questions about modifying the human body and mind.

• Gene Editing: Techniques such as CRISPR allow scientists to alter DNA sequences, potentially correcting genetic disorders or enhancing certain traits.

• Epigenetics: The study of changes in gene expression that do not involve alterations to the DNA sequence itself. Environmental factors such as stress, diet, and exposure to toxins can affect epigenetic markers, influencing how genes are expressed.

Example: Epigenetic changes can be triggered by early childhood experiences, affecting the risk of developing mental health disorders later in life.

Behavioral Genetics and Twin Studies

Behavioral genetics examines the relative contributions of genes and environment to individual differences in behavior.

• Twin Studies: Compare identical (monozygotic) twins, who share 100% of their genes, with fraternal (dizygotic) twins, who share about 50% of their genes, to estimate heritability.

• Heritability: The proportion of variation in a trait within a population that can be attributed to genetic differences. Heritability estimates range from 0 (no genetic contribution) to 1 (entirely genetic).

• Example Heritability Estimates:

  • Depression & Anxiety in identical twins: 0.76

  • Depression & Anxiety in fraternal twins: 0.48

Example: If identical twins are more similar in a trait than fraternal twins, this suggests a genetic influence.

Adoption Studies

Adoption studies compare adopted children to their biological and adoptive parents to disentangle genetic and environmental influences.

• Nature vs. Nurture: If a trait is more similar to biological parents, genetics play a larger role; if more similar to adoptive parents, environment is more influential.

Natural Selection

Natural selection is a key concept in evolutionary psychology, explaining how certain traits become more common in a population over generations.

• Variation: Individuals within a species show variation in traits.

• Selection: Traits that enhance survival and reproduction become more common.

• Adaptation: Over time, populations evolve as advantageous traits accumulate.

Example: The development of larger brain regions in humans compared to ancestors is thought to be an adaptive trait.

Cells of the Nervous System

Types of Cells

The nervous system is composed of specialized cells that transmit and process information.

• Neurons: The primary signaling cells, responsible for transmitting electrical and chemical signals throughout the body.

• Glial Cells: Support neurons by providing structural support, nutrition, and insulation. Types include astrocytes, microglia, and oligodendrocytes (which produce myelin).

• Myelin: A fatty substance that insulates axons, increasing the speed of electrical signal transmission.

Example: Multiple sclerosis is a disease in which myelin is damaged, leading to impaired neural communication.

Neural Communication

Neurons communicate via electrical impulses and chemical signals.

• Resting Membrane Potential: The difference in electrical charge across the neuron's membrane when not firing, typically around -70 mV.

• Action Potential: A rapid change in membrane potential that travels along the axon, allowing the neuron to transmit a signal.

• Ion Movement: Sodium (Na+) and potassium (K+) ions move across the membrane, generating electrical changes.

Equation:

$V_{rest} \approx -70\ \text{mV}$

Example: When a neuron is stimulated, Na+ channels open, causing depolarization and the initiation of an action potential.

Neurotransmitters

Major Neurotransmitters and Their Functions

Neurotransmitters are chemical messengers that transmit signals across synapses between neurons.

• Glutamate (GLU): The main excitatory neurotransmitter in the brain, involved in learning and memory.

• GABA (Gamma-Aminobutyric Acid): The main inhibitory neurotransmitter, reducing neuronal excitability.

• Acetylcholine (ACh): Involved in muscle contraction, learning, and memory.

• Dopamine (DA): Associated with reward, motivation, and motor control. Imbalances are linked to Parkinson's disease and schizophrenia.

• Norepinephrine (NA): Involved in arousal and alertness.

• Epinephrine (A): Also known as adrenaline, involved in the fight-or-flight response.

• Serotonin (5-HT): Regulates mood, appetite, and sleep. Low levels are associated with depression.

Neurotransmitter	Main Function	Associated Disorders
Glutamate	Excitatory signaling, learning, memory	Excess: excitotoxicity (e.g., stroke)
GABA	Inhibitory signaling	Deficiency: anxiety, epilepsy
Acetylcholine	Muscle movement, memory	Deficiency: Alzheimer's disease
Dopamine	Reward, motivation, movement	Deficiency: Parkinson's; Excess: schizophrenia
Norepinephrine	Arousal, alertness	Imbalance: mood disorders
Serotonin	Mood, sleep, appetite	Deficiency: depression

Example: Medications for depression often target serotonin levels to improve mood.

Additional info: Some content, such as the ethical implications of gene editing and the details of action potential propagation, was expanded for academic completeness.